Circuit arrangement for driving an inductive load

ABSTRACT

A circuit arrangement for driving an inductive load is connectable to a load terminal. A first MOS field effect transistor is connected between a terminal for a high potential of a first supply voltage source and the load terminal. A series connection with a freewheeling diode and a second MOS field effect transistor has its freewheeling diode connected between the load terminal and a second terminal for a low potential of the first supply voltage source. The freewheeling diode has its cathode connected to the load terminal. A series connection with a reverse-biased zener diode and a forward-biased diode is connected between the drain and gate terminals of the first MOS field effect transistor. A first control signal terminal is connected to the gate terminal of the second MOS field effect transistor and via an AND circuit to the gate terminal of the first MOS field effect transistor.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a circuit arrangement for driving a loadconnectable to a load terminal, having a first MOS field effecttransistor connected up between a first terminal for a high potential ofa first supply voltage source and the load terminal and having afreewheeling diode connected up between the load terminal and a secondterminal for a low potential of the first supply voltage source, thefreewheeling diode having its cathode connected to the load terminal.

Such a circuit arrangement is known from DE 10 2014 219 048 A1. Theinductive loads to be driven can be any type of magnetically operatedactuators such as, for example, fuel injection valves or motors, as areused diversely in a motor vehicle.

Such circuit arrangements are usually operated, as depicted in FIG. 4 ofDE 10 2014 219 048 A1, such that the MOS field effect transistor isclosed by means of driving via a control circuit, which can be realizedas a microprocessor, for example, as a result of which the inductiveload is supplied with current from the supply voltage source via theswitch realized by the MOS field effect transistor. The current in thiscase rises to a first prescribed threshold value, whereupon the fieldeffect transistor is opened again and the magnetic energy stored in theinductive load dissipates as a result of an induced flow of current viathe freewheeling diode, until the current reaches a second, lowerthreshold value, whereupon the field effect transistor is closed again.This is continued periodically, so that this pulsed operation results ina mean flow of current taking place in the inductive load and theresultant holding current keeps the magnetic actuator to be driven inthe desired position, for example a fuel injection valve remains open.If the field effect transistor is subsequently turned off, the magneticfield in the inductive load dissipates almost completely by means of acurrent via the freewheeling diode.

Although a circuit arrangement according to DE 10 2014 219 048 A1 is ofrelatively simple design with only a few components and has only oneconnection to the inductive load, the final dissipation of the magneticenergy stored in the inductive load is possible only by means of a flowof current via the freewheeling diode with its low forward voltage,which means that this can take an undesirably long time.

A broadening according to DE 10 2007 006 179 A1 can avoid this problem.In FIG. 3 therein, that terminal of the inductive load that is notconnected to the load terminal is connected to the reference-groundpotential via a further MOS field effect transistor and additionally tothe first terminal for a high potential of the first supply voltagesource via a further forward-biased diode. The load terminal is moreoverconnected to the terminal for a high potential of a second supplyvoltage source via a reverse-biased diode and a third MOS field effecttransistor, the voltage of the second supply voltage source being lowerthan the voltage of the first supply voltage source by a factor of 2 to3.

If such a circuit arrangement for driving an inductive load is operatedas shown in FIG. 5 of DE 10 2007 006 179 A1, closing of the first andsecond MOS field effect transistors will initially result in a currentfrom the first supply voltage source flowing through the inductive load,wherein this current rises relatively quickly on account of the highvoltage of the first supply voltage source, until it reaches a firstthreshold value. The first MOS field effect transistor is then closed,whereupon the magnetic field stored in the inductive load begins todissipate by means of a flow of current via the first diode and thesecond MOS field effect transistor, until the current reaches a second,lower threshold value, whereupon the third MOS field effect transistoris now turned on, however, and consequently only the distinctly lowervoltage of the second supply voltage source is then applied to theinductive load. The current now begins to rise again, until it reachesthe first threshold value again, whereupon the third MOS field effecttransistor is turned off again.

This process is now continued periodically again, until the inductiveload is to be turned off completely, which is effected by opening boththe third and the second MOS field effect transistor, whereupon themagnetic energy stored in the inductive load now dissipates as a resultof a flow of current via the first and second diodes back to the firstsupply voltage source, the distinctly higher voltage value of the firstsupply voltage source meaning that the decrease in current is effecteddistinctly more quickly, as can also be seen from the slopes of thecurrents in FIG. 5 of DE 10 2007 006 179 A1.

The price of this advantage, however, is that there are distinctly morecomponents in the circuit arrangement and additionally the inductiveload, which in a motor vehicle usually needs to be connected to acontroller containing the circuit arrangement by means of appropriatelines, now needs to be connected via two such lines, meaningcorrespondingly higher complexity. However, it is desirable to avoidadditional lines in the wiring harness and power switching elements,which have to carry high currents.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to specify a circuitarrangement for driving an inductive load that requires only oneconnection to an inductive load and furthermore requires few powerswitching elements, but is capable of quickly dissipating a magneticfield stored in the inductive load.

The object is achieved by a circuit arrangement as claimed, andadvantageous developments are specified in the dependent claims.

The object is achieved by a circuit arrangement of the type in questionin which the drain and gate terminals of the first MOS field effecttransistor have a series connection comprising at least onereverse-biased zener diode and a forward-biased diode connected upbetween them and in which a control signal terminal is connected to thegate terminal of the second MOS field effect transistor and via an ANDcircuit to the gate terminal of the first MOS field effect transistor.

As a result of this measure, the turned-on second MOS field effecttransistor means that during the pulsed hold phase the freewheelingdiode is used as a current path to demagnetize the inductive load,whereas during the turn-off process the second MOS field effecttransistor can be opened, so that the decrease in current is effected bymeans of the first MOS field effect transistor, which, on account of thevoltage induced in the inductive load on account of the turn-offprocess, produces a current path via the first zener diode and a Millercapacitance of the first MOS field effect transistor that turns on thefirst MOS field effect transistor again at this high voltage, so thatthe magnetic field in the inductive load can quickly dissipate.

In an advantageous development of the circuit arrangement according tothe invention, the second MOS field effect transistor has a first loadpath terminal and a second load path terminal, which is connected to thesecond terminal for the low potential of the first supply voltagesource, and also a gate terminal, wherein the first load path terminaland the gate terminal have the load path of a third MOS field effecttransistor connected up between them, the first control signal terminalbeing connected to the gate terminal of the latter via an invertercircuit.

This advantageous connecting-up of the second and third MOS field effecttransistors results in the third MOS field effect transistor beingturned on when the second MOS field effect transistor is turned off,which means that the second MOS field effect transistor is turned offvery quickly and hence the conductive path via the first MOS fieldeffect transistor is set up very quickly, so that the magnetic fieldstored in the inductive load can quickly dissipate.

In an advantageous form of the circuit arrangement according to theinvention, the second and third MOS field effect transistors are in theform of n-MOS field effect transistors that have a respective substratediode and are connected up such that the substrate diodes are connectedup with reverse polarity in relation to the freewheeling diode.

This prevents conductive paths from arising on account of the samepolarity of the substrate diodes and the freewheeling diode if the n-MOSfield effect transistors were to be connected up in the usual manner.

In a development of the circuit arrangement according to the invention,the first control signal terminal is connected to the gate terminal ofthe second and third MOS field effect transistors via a first and asecond driver circuit, respectively.

This allows logic levels to be used to drive the two MOS field effecttransistors and still allows the requisite voltages for these powertransistors to be provided.

In an advantageous form of the circuit arrangement according to theinvention, the gate terminal of the third MOS field effect transistor isconnected to the second terminal for a low potential of the supplyvoltage source via a first resistor, for the purpose of connecting saidsecond terminal to ground, and to the output of the second drivercircuit via a second resistor, for the purpose of current limiting.

In a further advantageous configuration of the circuit arrangement, theoutput of the second driver circuit is connected to the second terminalfor the low potential of the first supply voltage source via areverse-biased second diode. This serves as protection against negativevoltages at the output of the second driver circuit.

Likewise to protect against negative voltages, the gate terminal of thethird MOS field effect transistor is connected to the first loadterminal of the second MOS field effect transistor via a reverse-biasedzener diode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The invention is intended to be explained in more detail below on thebasis of an exemplary embodiment with the aid of figures. In the figureshere:

FIG. 1 shows a block diagram of a circuit arrangement according to theinvention,

FIG. 2 shows an MOS field effect transistor whose drain terminal isconnected to its gate terminal via at least one reverse-biased zenerdiode,

FIG. 3 shows a circuit diagram of a broadened circuit arrangementaccording to the invention,

FIG. 4 shows current and voltage profiles during a driving process foran inductive actuator.

DESCRIPTION OF THE INVENTION

In the block diagram of FIG. 1, the first terminal UV of a first supplyvoltage source VSQ1 is connected to a first load terminal of a powerswitching element 1, which as shown in FIG. 2 is in the form of a firstMOS field effect transistor T1. The second load terminal of the firstMOS field effect transistor T1 is connected to a node INJ_HS that issecondly connected to the second terminal GND for a low supply voltagepotential of the first supply voltage source VSQ1 via a reverse-biasedfreewheeling diode FD and a second power switching element 2 connectedin series therewith. The node INJ_HS additionally has the first terminalof an inductive load IL connected to it, the second terminal of theinductive load IL being connected to the second terminal GND of thefirst supply voltage source VSQ1.

In the example of FIG. 1, the inductive load IL is depicted with aninductance L, a non-reactive resistance RL1 connected in seriestherewith and a second resistance RL2 connected in parallel with saidseries connection as an equivalent circuit diagram.

A first control terminal SA1 is connected firstly to the controlterminal of the second power switching element 2 and secondly via an ANDgate AND to the control terminal of the first MOS field effecttransistor T1. A further input of the AND gate AND has the output of anOR gate OR connected to it, the two inputs of which are connected to asecond and a third control terminal SA2, SA3, respectively.

In a manner according to the invention, the first load terminal of thefirst power switching element 1, which corresponds to the drain terminalof the first MOS field effect transistor T1, and the control terminal ofthe first power switching element 1, which corresponds to the gateterminal of the first MOS field effect transistor T1, have the seriesconnection comprising a reverse-biased first zener diode ZD1 and aforward-biased first diode D1 connected between them.

The operation of the circuit arrangement as shown in FIG. 1 with a firstpower switching element 1 as shown in FIG. 2 will be explained in thiscase on the basis of FIG. 4 by means of the current and voltage profilesdepicted therein at particular points in the circuit arrangement.

When the first signal terminal SA1 has a signal at a particular levelapplied to it—for example a TTL level of 5 volts—this turns on thesecond power switching element 2. If additionally one of the two furthersignal terminals SA2 or SA3 has a high level applied to it, the secondinput of the AND gate AND also has a high level applied to it, so thatthe signal CMD_HS at the output of the AND gate AND has a high level, asdepicted in a first time range in the lower graph in FIG. 4. Thislikewise turns on the first power switching element 1, which is formedby means of the first MOS field effect transistor T1, so that a currentnow flows from the first supply voltage source VSQ1 to the inductiveload IL via the first power switching element 1, the result being acurrent profile as shown in the upper graph in FIG. 4 that shows thetypical experimentally rising current profile for an inductance.

This current is measured and is compared with a first threshold value,this being effected in a control circuit, not depicted, and arrival atthis threshold value results in a LOW level at the signal terminal S2 orS3 previously switched to HIGH likewise switching the signal CMD_HS atthe output of the AND gate AND to LOW, as can be seen in the lower graphin FIG. 4.

This turns off the first MOS field effect transistor T1 again, as aresult of which the magnetic field built up in the inductive load ILdissipates by virtue of an induced voltage bringing about a flow ofcurrent that is effected via the freewheeling diode FD and the secondpower switching element 2.

In the pulse-modulated mode that now follows, the signal at the controlsignal input SA2 and SA3 is periodically switched on and off again atequidistant intervals, as can be seen in the lower graph in FIG. 4,resulting in a current profile as depicted in the upper graph in FIG. 4.The middle graph in FIG. 4 depicts the voltage profile at the nodeINJ_HS.

When the inductive load IL is finally intended to be turned off, thesignal at the first control terminal SA1 is switched to LOW, so that thesecond power switching element 2 opens and the AND gate AND is likewiseused to turn off the first power switching element 1. As a result, theinductive load IL, in which a magnetic field is in turn dissipated,means that a negative voltage is built up at the node INJ_HS, saidvoltage rising until the zener diode ZD1 begins to turn on. The gate ofthe first MOS field effect transistor T1 is charged by means of theMiller capacitance thereof and consequently the first MOS field effecttransistor T1 is turned on again. The voltage at the node INJ_HS is heldat the high level required for the zener diode ZD1 to be on, as a resultof which the inductive load IL can quickly discharge.

If the zener voltage of the first zener diode ZD1 is 63 volts, forexample, the voltage across the first diode D1 connected in seriestherewith is 0.6 volt, the Miller plateau voltage is 3 volts and thevoltage of the first supply voltage source VSQ1 is 12 volts, a necessaryvoltage for turning back on the first MOS field effect transistor T1 atthe node INJ_HS is12 V−63 V−0.6 V−3 V=−54.6 V,

which can be seen in the middle graph in FIG. 4.

It is thus possible to achieve fast dissipation of the magnetic energystored in the inductive load IL by using just two power switchingelements T1, T2 and just one connecting line between them and theinductive load IL.

FIG. 3 shows not only the circuit components of the circuit arrangementaccording to the invention, as are already depicted in FIG. 1, but alsoan advantageous form of the second power switching element 2 that allowsvery fast opening of the second power switching element 2.

The second power switching element 2 is in this case formed by means ofa second MOS field effect transistor T2 whose terminal connected to thefreewheeling diode FD is connected to the gate terminal of a third MOSfield effect transistor T3 via the load path thereof. The controlterminal of the third MOS field effect transistor T3 is in this caseconnected to the first control terminal SA1 via an inverter IV, so thatthe second and third MOS field effect transistors T2, T3 are each drivenin the opposite sense.

Thus, when the second MOS field effect transistor T2 is turned off, thethird MOS field effect transistor T3 is at the same time turned on, sothat the second MOS field effect transistor T2 is quickly and reliablyoff.

Both the second and the third MOS field effect transistor T2, T3 havetheir source terminals connected to the anode of the freewheeling diodeFD, as a result of which the substrate diodes thereof are connected withthe opposite polarity to the freewheeling diode FD, so that this cannotresult in a conductive path.

In the exemplary embodiment of FIG. 3, the first control terminal SA1 isconnected to the gate terminal of the second MOS field effect transistorT2 via a first driver circuit 3 and a voltage divider R3, R4. The outputof the inverter IV is connected to the gate terminal of the third MOSfield effect transistor T3 via a second driver circuit 4 and a currentlimiting resistor R2, this gate terminal additionally being connected tothe second terminal for a low potential of the first supply voltagesource VSQ1 via a first resistor R1 for the purpose of safely connectingto ground.

The output of the second driver circuit 4 is connected to the secondterminal for a low potential GND of the first supply voltage source VSQ1via a second diode D2, which is reverse-biased, for the purpose ofprotecting against negative voltages. The gate/source junction of thethird MOS field effect transistor T3 is likewise bypassed by means of asecond zener diode ZD2 for the purpose of protecting against negativevoltages on the gate terminal of the third MOS field effect transistorT3.

The driver circuits 3, 4 are supplied with power by a second supplyvoltage source VSQ2.

The invention claimed is:
 1. A circuit arrangement for driving aninductive load that is connectable to a load terminal, the circuitarrangement comprising: a first MOS field effect transistor connected upbetween a first terminal for a high potential of a first supply voltagesource and the load terminal; a series circuit having a freewheelingdiode and a second MOS field effect transistor, said freewheeling diodebeing connected up between the load terminal and a second terminal for alow potential of the first supply voltage source, and said freewheelingdiode having a cathode connected to the load terminal; said first MOSfield effect transistor having drain and gate terminals, and a seriescircuit with at least one reverse-biased first zener diode and aforward-biased first diode connected up between said drain and gateterminals; and a first control signal terminal connected to a gateterminal of said second MOS field effect transistor and an AND circuitconnected between said first control signal terminal and a gate terminalof said first MOS field effect transistor.
 2. The circuit arrangementaccording to claim 1, wherein: said second MOS field effect transistorhas a first load path terminal, a second load path terminal, and saidgate terminal; said second load path terminal is connected to theterminal for the low potential of said first supply voltage source; saidfirst load path terminal and said gate terminal have a load path of athird MOS field effect transistor connected there between; and saidfirst control signal terminal is connected to a gate terminal of saidthird MOS field effect transistor via an inverter circuit.
 3. Thecircuit arrangement according to claim 2, wherein said second MOS fieldeffect transistor and said third MOS field effect transistor are n-MOSfield effect transistors, each having a respective substrate diode andconnected up such that said substrate diodes are connected up withreverse polarity in relation to said freewheeling diode.
 4. The circuitarrangement according to claim 2, wherein said gate terminal of saidthird MOS field effect transistor is connected to the first loadterminal of said second MOS field effect transistor via a reverse-biasedsecond zener diode.
 5. The circuit arrangement according to claim 2,further comprising a first driver circuit connecting said first controlsignal terminal to the gate terminal of said second MOS field effecttransistor and a second driver circuit connecting said first controlsignal terminal to said third MOS field effect transistor.
 6. Thecircuit arrangement according to claim 5, wherein the gate terminal ofsaid third MOS field effect transistor is connected to the terminal forthe low potential of said first supply voltage source via a firstresistor and to an output of said second driver circuit via a secondresistor.
 7. The circuit arrangement according to claim 5, wherein anoutput of said second driver circuit is connected to the terminal forthe low potential of said first supply voltage source via areverse-biased second diode.
 8. The circuit arrangement according toclaim 5, wherein the gate terminal of said third MOS field effecttransistor is connected to the terminal for the low potential of saidfirst supply voltage source via a first resistor and to an output ofsaid second driver circuit via a second resistor; and an output of saidsecond driver circuit is connected to the terminal for the low potentialof said first supply voltage source via a reverse-biased second diode.9. The circuit arrangement according to claim 8, wherein said gateterminal of said third MOS field effect transistor is connected to thefirst load terminal of said second MOS field effect transistor via areverse-biased second zener diode.